KA 4: Ante- and postnatal screening (a) Antenatal screening (c) Pedigree charts (b) Postnatal screening

Learning Outcomes Identify the disorder that is tested for post-birth Describe how this disorder is tested for and diagnosed State the treatment for this disorder Describe how this disorder can be inherited State what is meant by an ‘inborn error of metabolism’

Metabolic disorder: PKU (Inheritance) Phenylketonuria (PKU) is the only inherited disorder that can be treated It is categorised as an “inborn error of metabolism” A genetic disorder caused by a single defective gene. The gene tends to code for a protein (an enzyme) in a metabolic pathway It is condition characterised by a person’s inability to break down the amino acid phenylalanine into tyrosine. The affected individual has to inherit a copy of the defective gene from both parents (autosomal recessive disorder) A person with only one gene will not display any physical characteristics of the condition. Instead they are known as a carrier:

Metabolic disorder: PKU (Inheritance) Normal gene: NN PKU gene: nn Genetic Cross of 2 carriers Parents: Mum: Nn Dad: Nn Gametes: N or n N or n F1: normal: carriers: affected: N n NN Nn Nn nn 1 2 1 The child has a 25% (1 in 4) chance of developing PKU

Metabolic disorder: PKU (Screening) All new-born babies are screened for PKU Their blood is tested for an excess of phenylalanine. PKU sufferers (individuals with high levels of phenylalanine in their blood) are then placed on a restricted diet containing the minimum quantity of phenylalanine needed for normal growth. If a person follows this restricted diet, especially during childhood, mental deficiency is prevented 

Other new-born screening tests Galactosaemia What is it? A rare genetic metabolic disorder that affects an individual's ability to metabolize the sugar galactose properly. THE TEST: A galactosemia test is a blood test (from the heel of the infant) or urine test that checks for three enzymes that are needed to change galactose sugar that is found in milk and milk products-into glucose, a sugar that your body uses for energy. A person with galactosemia doesn't have one of these enzymes. This causes high levels of galactose in the blood or urine.

Other new-born screening tests Congenital hypothyroidism What is it? A thyroid hormone deficiency condition. If untreated for several months after birth, severe congenital hypothyroidism can lead to growth failure and permanent intellectual disability. THE TEST: part of the newborn screening program which involves measuring TSH or thyroxine (T4) levels on the second or third day of life (Heel prick). Diagnosis is confirmed if the TSH is high, or the T4 low.

Other new-born screening tests Amino acid disorders

Other new-born screening tests Amino acid disorders What is it? Amino acid disorders (AAs) are a group of rare inherited conditions. They are caused by a particular enzyme (a chemical found naturally in the body) being faulty or missing. This leads to problems breaking down certain amino acids. Amino acids are the building blocks of proteins. This disorder leads to a build up of unwanted chemicals that can cause damage to vital parts of the body such as the liver. THE TEST: heel prick test, to test for the presence of high levels of amino acids and low levels of enzymes

Learning Outcomes Identify the disorder that is tested for post-birth Describe how this disorder is tested for and diagnosed State the treatment for this disorder Describe how this disorder can be inherited State what is meant by an ‘inborn error of metabolism’